Research On Early Age Concrete Humidity And Shrinkage Cracking Of Doubled-block Ballastless Track

The double-block ballastless track is made of concrete,which suffers from the adverse impact of the natural environment.Under the influence of its own hydration and drying,the internal humidity of track structure will form an uneven distribution state,and the uneven distribution of humidity will inevitably cause the non-uniform shrinkage or expansion deformation of concrete materials.Due to the large volume of double-block ballastless track and the constraint between the lower foundation and the components,the shrinkage deformation cannot develop freely,which will cause uneven shrinkage stress field inside the track structure and then cause cracking.Under the action of various incentives,the cracks of ballastless track will gradually expand into obvious cracks and affect its durability.Therefore,it is of great significance for the design and maintenance of ballastless track to establish the relationship between the humidity field and the strain field of double-block ballastless track,and to explore the stress distribution rule and shrinkage and cracking mechanism of track slab.The main research contents and conclusions of this paper are as follows:(1)By collecting and sorting out relevant domestic and foreign literatures,the types and causes of shrinkage cracks on track slab are summarized.(2)The mathematical model of concrete humidity field and the two-stage development model of concrete shrinkage based on the change of humidity were established.The software Comsol was used to solve the theoretical model.The calculation results showed that the shrinkage strain and the change of humidity had a good synchronization.(3)In view of the phenomenon that the track slab of double-block ballastless track on subgrade is more likely to produce shrinkage cracks,the early-stage shrinkage model of double-block ballastless track is established to obtain the distribution and development rules of humidity field,cement hydration field and shrinkage strain-stress field of double-block ballastless track under the action of self-drying and drying.The analysis shows that the tensile stress of the track bed plate near the corner point of the rail components and between the double-block sleepers is large,and it is easy to form early shrinkage cracks.(4)For the problem that it is difficult to explain the free microcrack in the track slab by using the macroscopic model,from the perspective of microstructure,the shrinkage and deformation microstructure of early concrete considering the performance difference between aggregate and mortar is established to explain the generation mechanism of the free microcrack in the track slab.